Optical borate glass of high chemical resistance and process of making same

ABSTRACT

An optical borate glass of high chemical resistance, with negative anomalous partial dispersion, refraction index ne between 1,65 and 1,79, and Abbe number Nu e between 40 and 30 is composed of boron trioxide, lead oxide, and aluminum oxide. It may additionally contain lithium, sodium, and/or potassium oxides, zinc oxide, zirconium dioxide, tantalum pentoxide, and, if desired, antimony trioxide and/or bismuthum trioxide.

Broemer et al.

Ernst Leitz G.m.b.H., Wetzlar, Germany Filed: May 15, 1973 Appl. N0.: 360,418

Assignee:

Foreign Application Priority Data May 15, 1972 Germany 2223564 US. Cl. 106/47 Q; 106/47 R Int. Cl..... C03C 3/14; C03C 3/00; C03C 3/30 Field of Search 106/47 Q, 47 R References Cited UNITED STATES PATENTS 6/1950 Sun et al 106/47 Q 8/1961 Broemer et al. 106/47 Q Dec. 30, 1975 3,149,984 9/1964 Faulstich 106/47 R 3,307,929 3/1967 Trap 106/47 R 3,480,453 11/1969 Reid et al 106/47 R 3,486,915 12/1969 Broemer et a1. 106/47 R 3,510,325 5/1970 Broemer et al. 106/47 R FOREIGN PATENTS OR APPLICATIONS 863,352 3/1961 United Kingdom 106/47 Q 4,424,420 10/1969 Japan 106/47 Q Primary ExaminerWinston A. Douglas Assistant Examiner-Mark Bell Attorney, Agent, or FirmErich M. H. Radde [57] ABSTRACT lead oxide, and aluminum oxide. It may additionally contain lithium, sodium, and/or potassium oxides, zinc oxide, zirconium dioxide, tantalum pentoxide, and, if desired, antimony trioxide and/or bismuthum trioxide.

23 Claims, No Drawings OPTICAL BORATE GIL ASS OF I-IIGI-I CHEMICAL RESISTANCE AND PROCESS OF MAKING SAME BACKGROUND OF THE INVENTlON 1 Field of the lnvention The present invention relates to an optical borate glass and more particularly to an optical borate glass of high chemical resistance with negative anomalous partial dispersion, refractiveindices' n betweeii 1.65and 1.79, and Abbe numbersv between 40an'd a method or manufacturing same.

2 Description of the Prior Art 30, and to Recently the need'for opticahglass of a high index of refraction and a low Abbe number which, as additional parameter,"have a negative anomalous partial dispersion, has increased greatly due 'to'recalculations of optical systems. In this connection,'it-is of decisive importance to improve the possibilities of correction of the optical systems by the use of optical glasses of predetermined anomalous partial dispersion. Detailsconcerning the importance, the use and the nomenclature of glasses having anomalous partial dispersion values are set forth in German Pat. No. 1,496,563. I However, it has proven to be very difficult to produce, by melting, glasses having the aforesaid physical properties because they do not ppssessother properties which are absolutely required for utilizing them in highgrade optical systems, such as, for instance, lack of color and high chemical resistance.

Glasses of this type which have become known heretofore either have insufficient chemical resistance or else a disturbing color cast. Due to their insufficient chemical resistance, they are not only unsuitable for use as outer lenses in modern optical systems, but they, are also responsible for causing a very high percentage of rejects when mechanically assembling them.

SUMMARY OF THE INVENTION It is one object of the present invention to provide an optical borate glass of superior chemical resistance which, in addition to a refractive index n between 1.65 and 1.79 and an Abbe numbery between 40 and, 30,

also has a negative anomalous partial dispersion but I centages also indicated therein.

. between 2.0 and 6.0 percent, by weight, of zirconium oxide (Zro 1 between 2 and 15 percent, by weight, of tantalum I oxide-(Ta o and between 8 and 16percent, by weight, of antimony oxide (sb o la'nd/orbismuthum oxide"(Bi' -O j The process ofrrianufacturing the glasses of the-pres-- DESCRIPTION OF- THE PREFERRED EMBODIMENTS The following examples serve to illustrate the present invention without, however, limiting the same thereto. Thus a number of glasses according to the present invention are given in the following Tables, The refractive index n the Abbe number 11,; (reciprocal of the dispersion), and the amount of the anomalous partial dispersion Av are also indicated in said Tables.

l n Table l, examples are given for the pure ternary Table 1 (weight Glass No.2 1 2 3 8,0, 38.5 38.5 38.5 PbO 56.5 51.5 46.5 141,0, 5.0 10.0 15.0

which is free of the disadvantages of the known glasses.

Another. object of the present invention is toprovide a simple and effective process of making such a valuable optical borate glass.

Other objects of the present invention and advantageous features thereof will become apparent as the description proceeds.

in principle these objects are achieved by providing a glass which contains between 26 and 39 percent, by weight, of boron trioxide (B 0 between 32 and 57 percent, by weight, of lead oxide (PhD), and

between 5 and 19 percent, by weight, of aluminum oxide (A1 0 According to a specific embodiment of the present invention the glass can, in addition, contain the following components in the quantities indicated:

Between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals lithium (Li,O), sodium (Na O), and potassium (K 0),

between 0.8 and 8.0 percent, by weight, of zinc oxide in these compositions the proportion of boron trioxide (B 0 was left constant in each case while that of aluminum oxide- (Al O )was increased at the expense of the proportion'of lead oxide (PbO) by 5 percent, by weight, each time. Thereby, in addition to a decrease in the refractive index and a corresponding increase in the Abbe number, the absolute value ofthe anomalous partial dispersion increases.

In Table'2, the example given in Table 1 under Glass No. 3 is modified by partially replacing lead oxide by an alkali metal oxide.

- It iseVident that with such partial substitutions,-a Table 5 cominued predetermined fine adjustment of the opticalposition parameters canb'e' effected. l' 6 Of course, it is understood that the useof the alkali ass f 1 metal :oxides is not limited to the addition 'of'a-single 5 I alkali metal oxide only; rather, it is also possible to add 2 5-1 two ,ormore oxides together for partially replacing'the K v, 3.2 3I8 3:0 lead oxide. 4 1

In vTable 3,.zinc oxide is added to thethree compo- 4 4 1 nent startingglass. 'lnthiscasealso starting fromthe Thereby, the total proportion of the sum of zircocomposition given as Glass'No. 3 in Table 1 the zinc nium, dioxide-plus tantalum pentoxide (ZrO, Ta o oxide (ZnO) is substituted inpartfor equal percenthas been increased from l0. 0perc ent, by weight, in the ages, by weight,'of lead oxide (PbO). g I composition of Example l5, to-l4.0 percent, by weight,

Table/3 I Y I, in the composition of Example l 6, and finally to 16.0 v, i percent, by weight, in the composition of Example 17, (weight I whereby the zirconium dioxide and tantalum pentoxide Glass No.: 7 8 9 are substituted for the same proport1on, by weight, of gig 32-; 33:2 boron trioxide (B 0 On the other; hand, the weight Al,0, 15.0 15:0 5: percentages of lead oxide (PbO) and aluminum oxide Zno (A50 were left constant. g n 1 L669 16689 1.6659 F1nally, 1n Tablet), 1n add1t1on to the replacement v, 39.2 9;; 401 compounds z1rcon1u m d1ox1de (D0,) and tantalum pentoxide (Ta,0,) mentioned heretofore, there are furthermore alsoused in addition antimony trioxide v 515,0 and bismuthum trioxide (Bi,05), alone or in Glafs 7 has 23 negat'we anomalous P l" combination. As a result thereof further possibilities of tlal'dlspel'slon of P p E n However, this combinations for the three optical parameters n 11,, does not mean that h1gher negative values for the Av, and A are made avai|ab|e Table 6 Y (weight 76' Glass No.: 18 19 20 21 22 13,0, 33 5' 33.5 31.0 4 31.0 31.0 P00 42 5 42.5 40.0 4 40.0 32.0v 411,0, 5.0 5.0 10.0 10.0 10.0 210, 3.0 3.0 3.0 3.0 3.0 Ta O. 80 8L0 8.0 8.0 8.0

s0 8.0 8.0 131.0, 3.0 I I y 0.0 80 n, l.7500 1.7652 1.7433 l.;.75l3 1.7457 1!, 32.7 32.3 33.0 32.9 32.6 Av, -3.5 -'2.2 3.0 l.9 4 l.8

f f a Value of would not be comprised A preferred glass in accordance with the present y mventloninvention which has the same optical properties as an m Table 4 tantalum P hp5) bcen 45 ordinary commercial glass',but w'hichin addition is also added l tome component verystable chemically; in contradistinction to the base glass while in Table 5 zirconium dioxide (21-0,) I known' glass i dffth fouowing composition (in has also been added. 2 1 cent by i Table'4 .(weight 0133 310.; 10 11 12 13 14 '13,o,' 35.0 35.0 1 30.0 30.0 26.0 PbO 45.0 45.0 50.0 1 50.0 57.0 411.0, 10.0 5.0 10.0 5.0 3.0 33,0, 10.0 15.0 10.0 15.0 9.0 11, 1.7221 1.7414 1.7461 1.7766 mm .v. 34.5 33.4 32.9 31.3 30.0 Av, -3.4 -3.3 -2.4 -2.3 -0.5

Table 5 GIuINO.: 7 16' l7 1 B o, 35.0 31.0 29.0 PbO r 39.0 P00. 45.0 v 45.0 45.0 a 111,0, 7 13.5 A10, 10.0 10.0 10.0 V 1.1.0 0.2 Zr?) 20 4.0 6.0 113,0 2.3 T0, 0.0 10.0 ZnO 0.3 v

Said glass No. 25 was investigated together with a commercial glass of the same optical position as to its chemical resistance according to a method published by H. BREDOW in the journal Glass-Email-Keramo- Technik, Vol. 10, No. 8, pages 297-299 (1959).

Thereby, the results set forth in Table 7 were obtained. I

Table 7 Solution residue (mg) (reduced values) Commercial Glass No. 25

glass I with respect to 0.1 N HNO z 193.0 63.0 with respect to standard acetate: 141.0 36.0

The measured values obtained show that the solution residue of glass No. 25 of this invention is several times lower than that of the commercial glass. In order to have a clear idea of the asserted value of these measurements, the glasses LaK 9 and SK 16, as very well known comparison glasses, are indicated with their corresponding solution residues. The term .reduced values" indicates the quotient resulting from the division of the solution residue in mg. and the specific gravity of the respective glass. Standard acetate is a standard acetate buffer solution of the pH is 4.62.

Table 8 Solution residue (rrig.) (reduced values) Comparison glasses: LaK 9 SK 16 with respect to 0.1 N HNO, 52.7 107.5 with respect to standard acetate: 80.0

temperature of about 1300 C. After melting down,

homogenization is effected with agitation for 60 minutes at about 1500 C. When complete freedom from bubbles has been obtained, the temperature of the melt is lowered to 1 120 C. and poured into preheated steel molds.

It is understood, of course, that, in accordance with the present invention and the claims annexed hereto, not only the glass compositions as given in the Tables can be melted to yield the desired optical borate glasses of high chemical resistance but that other compositions will also yield, on melting the valuable borat'e glasses of this invention, such as, for instance, compositions 6 which contain, in addition to the basic glass components boron trioxide, lead oxide, and aluminum oxide, up to 3.0 percent, by weight, ofat least one of the oxides of thealkali metals-lithium (Li), sodium (Na), and potassium (k but, when present, not less than 0.2 percent, by weight, of said oxides; and/or up to 8.0 percent, byweight, of zinc oxide (ZnO), but, when present, not less than 0.8 percent, by weight, thereof; and/or up to 6.0'percent, by weight, of zirconium dioxide (ZrO but, when present, notless than 2.0 percent, by weight, thereof; and/or up to 15.0percent, by weight, of tantalum pentoxide '(Ta O but, when present, not less than 2.0 percent, by weight, thereof; and/or up to 16.0 percent, by weight, of an oxide selected from the group consisting of antimony trioxide (Sb O and bismuthum trioxide (Bi O but, when present, not less than 8.0 percent, by weight, thereof.

We claim:

1. An optical borate glass of high chemical resistance, with negative anomalous partial dispersion and refractive indic'es n between 1. 65 and 1.79 and Abbe numbers v between 40 and 30, said glass consisting of between 26 and 39 percent, by weight, of boron trioxide (B 0 between 32 and 57 percent, by weight, of lead oxide between 5 and 19 percent, by weight, of aluminum Oxide up to 3.0 percent, by'weight, of at least one of the oxides of the alkali metals lithium (Li), sodium (Na), and potassium (K), but when present, not less than 2.0 percent, by weight, of said oxides;

up to 8.0 percent, by weight, of zinc oxide (ZnO), but, when present, not less than 0.8 percent, by weight, thereof; up to 600 percent; by weight, of zirconium dioxide 210, but, when present, not less than 2.0 percent, by weight, thereof;

up to 15.0 percent, by weight, of tantalum pentoxide (Ta O but, when present, not less than 2.0 percent, by weight, thereof; and up to 16.0 percent, by weight, of .a oxide selected from the group consisting of antimony trioxide (Sb O and bismuthum trioxide 131,0 but, when present, not less than 8.0 percent, by weight, thereof.

2. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B 0 between 32 and 57 percent, by weight, of lead. oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (A1 0 and between 0.2 and 3.0-percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K). g

- 3. The glass of claim 1, consisting of betweeen 26 and 39 percent, by weight, of boron trioxide (B 0 between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of-aluminum oxide (A1 0,) and between 0.8-and 8.0 percent, by weight, of zinc oxide-(ZnO). v

4. The glass of claim 1, consisting of between 26'and 39 percent, by weight, of boron trioxide (B 0 between 32 and '57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (A150,), between 0.2 and 3.0 percent, by

weight, of at least one of the oxides of the alkali metals selected from the. group. consisting of lithium-:(Li), sodium (Na), and potassium,(K), and between 0.8 and 8.0 percent, by 'weight,-of zinc oxidex(ZnO).

5. The glass of claim 1,; consisting of between 26 and tween 32and 57 percent, by weight, pf leadoxide (PbO), between 5 and l9percent, by weight, vof-aluminum oxide (Al O ),andbetween.-2 .0 and 6.0 percent, by weight, of zirconium dioxide: (Zr

6. The glass of claim 1,Tconsisting of=between 26- and 39 percent,-by weight, of boron trioxide (B 0 between 32- and 57 percent,.by weight; of lead oxide (Pb0), between Sand 19 percent, by weight, of\ aluminum oxide (A1 0 between 0.2 and 3.0, percent," by

weight, of at least one of the oxides of the alkali'metals' selected from the group consisting of lithium (M), sodium (Na), and potassium (K), and between 2.0 and 6.0 percent, by weight, ofzirconium dioxide (ZrO,).

7. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B 0 between 32 and 57 percent, by weight, of lead oxide (PbO), between Sand 19 percent, by weight, of aluminum oxide (M 0 between 0.8 and 8.0 percent, by weight, of zinc oxide(Zn0), and between 2.0,and 6.0 percent, by weight, of zirconium'dioxide (Zr0 .5

8. The glass of claim 1, consisting of between .26 and 39 percent, by weight, of boron trioxide (B 0 between 32 and, 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al,0 between 0.2 and 3.0 percent,,by weight, of at least one of the oxides of the alkali metals selected from the group consisting, of lithium (Li), sodium (Na), and potassium (K), between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO), and between 2.0 and 6.0 percent, by weight, of zirconium dioxide (Zr0,). I

I 9. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (8,0,), between-32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight,of aluminum oxide (Al,0,), and between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta,0,).

10. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide. (8,0, be-

tween 32 .and 57 percent, by weight, of leadoxide- (PbO), between 5 and 19 percent, by weight, of aluminum oxide (A1 0,), between 0.2 and 3.0v percent, by weight, of at least one of the oxides of thealkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), and between 2.0 and 15.0,. percent, by weight, of tantalum pentoxide 1 5) i l 1. The, glass of claim 1, consisting of between 26 and 39 percent, by weight, of borontrioxide (B 0 be- .39 percent, by weight, of boron trioxide, (B 0 bepercent, by weight, of zinc oxide (ZnO), and between 2.0 and 15.0 percent,by weight, of tantalum pentoxide (Ta' 0 1 13. The glass of claim 1, consisting'of between 26 and 39 percent, by weight, of boron trioxide (B 0 between 32 and- 57 percent, by weight, of-lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (A1 0 between 2.0 and 6.0 percent, by weight, of zirconium dioxide (Zr0,), and between 2.0 and 15.0 percent, by weight, of tantalum pentoxide 2 5) 14. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B 0 between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum: oxide (A1 0 between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li),

sodium (Na); and potassium (K),'between 2.0 and 6.0 percent, by weight, of zirconium dioxide (Zr-0,) and between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta,0,).

15. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B 0 between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al,0,), between 0.8 and 8.0 percent, by weight, of zinc oxide (Zn0.), between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO and between 2.() and 15.0 percent by weight, of tantalum pentoxide (Ta,0,).

16. The glass of claiml, consisting of between 26 and 39 percent, by weight, of boron trioxide (8,0,), between 32 and 57 percent, by weigh'tm of lead oxide (Pb0), between Sand 19 percent, by weight, of aluminum oxide (Al,0,), between 0.2 and 3.0"p ercent, by

weight, of at least one-of the oxides'ot' the alkali metals selected' from the group consisting of lithium (Li), sodium (Na),-and potassium (K), between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO), between 2.0 and 6.0 percent, by weight, of zirconium dioxide (Zr0,), andbetween 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta,0,).-

17. The'g'lass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B9 between 32'and 57'percent, by weightfof lead oxide (PbO), between 5 and 19 percent, by weight, of alumitween 32 and,57 percent, by weight, of lead oxide (Pb0), between Sand 19, percent, by weight, of aluminum oxide (Al,0 between 0.8 .and .8.'0 per'cent,.by weight, of zincoxide (ZnO), and between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta,0

12. The glass of claim l consisting of between 26and 39 percent, by weight,,.0lf' boron trioxide (B,0 between 32. and 57 percent byweight, of lead oxide (PbO), between 5 and ,l.9,;.percent, by weight, of aluminum oxide (A1 0,), between .0.2- .-and.3 .0 percent, by weight, of at least one of theoxides of the alkali metals selected from the group "consisting; of ,lithium (Li), sodium (Na), andpotassiumtKLbetween 0.8 and 8.0

num oxide (Al,0,), and between 8.0 and 16.0 percent, by weight, of at leastone oxide selected from the group consisting of antimony trioxide (Sb,0,) and bismuthum trioxide Bi,o, I

18. The glass of claim 1, consisting of between 26 and 39 percent, by weight, ofboron trioxide (8,0 between 32 and 57,. percent, by weight, of lead oxide (Pb0), betweeen 5 and 19 percent, by weight, of aluminum oxide A1,o, between 2.0 and. 6.0 percent, by

weight, of zirconium dioxide 1(Zr0,), and between 8.0 and 16.0 percent, byweight, of at least one oxide selected from the group consisting of antimony trioxide (Sb,0;,) and bismuthumtrioxide Bi,o,

19. The glass of claim 1, consisting of between 26 and 39 percent, .by weight, or boron trioxide (8 0,), between-32 .and 57 percent, by weight, of lead oxide (Pb0:),.between5 and 19 percent, by weight, of aluminumoxide (M 0 between 2.0 and 15.0 percent, by weight, of tantalum pentoxide Tap and between 8.0

- and 16.0 percent, by weight, of at least one oxide selected from thegroup consisting of antimony trioxide (Sb O and bismuthum trioxide (Bi O 20. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B between 32 and 57 percent, by weight, of lead oxide (PbO), between and 19 percent, by weight, of aluminum oxide (A1 0 between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta O and between 8.0 and 16.0 percent, by weight, of at least one oxide selected from the group consisting of antimony trioxide (Sb and bismuthum trioxide 2 3)- 21. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide B 0 between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (A1 0 between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO), between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta O and between 8.0 and 16.0 percent, by weight, of at least one oxide selected from the group consisting of antimony trioxide (Sb O and bismuthum trioxide (Bi O 22. An optical borate glass of high chemical resistance of the following composition:

-continued Component by weight zirconium dioxide(ZrO 2.0 tantalum pentoxide(Ta O 2.0,

23. In a process of manufacturing a glass of the composition of claim 1, the steps which consist essentially 111 a. melting a mixture of the oxides consisting of between 26 and 39 percent, by weight, of boron trioxide (B 0 between 32 and 57 percent, by weight, of lead oxide (PbO), and between 5 and 19 percent, by weight, of aluminum oxide (A1 0 up to 3.0 percent, by weight, of at least one of the oxides of the alkali metals lithium (Li), sodium (Na), and potassium (K), but, when present, not less than 2.0 percent, by weight, of said oxides; up to 8.0 percent, by weight, of zinc oxide (ZnO), but, when present, not less than 0.8 percent, by weight, thereof; up to 6.0 percent, by weight, of zirconium dioxide (ZrO but, when present, not less than 2.0 percent, by weight, thereof; up to 15.0 percent, by weight, of tantalum pentoxide (Ta O but, when present, not less than 2.0 percent, by weight, thereof; and up to 16.0 percent, by weight, of an oxide selected from the group consisting of antimony trioxide $13 0 and bismuthum trioxide (E 0 but, when present, not less than 8.0 percent, by weight, thereof at a temperature between about l300C. and about 1500C.,

b. homogenizing the molten mixture to produce a bubble-free melt,

c. cooling said mixture to about lC., and

d. casting the melt into preheated molds.

* t i F i PO-loso UNITED STATES PATENT OFFICE QERTlFlC/XTE OF, QGRRECTION Patent No. 3,929,495 Dated December 30, 1975 lnventofls) HEINZ BROEMER and NORBERT MEINERT Page 1 0f 2 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: 9

Column 4, line 11: The comma between "nium" and "dioxide" should be cancelled.

Q Column 4, last Table, Glass No. 25: In the heading of said Table "Glass no. should read Glass No.:

Column 5, Table continued: "Glass no." should read a Glass No.

Column 5, line 41: "is" should read of line 52: After "invention" there should be inserted is effected line 60: Before "poured" there should be inserted the melt is-.

Column 6 line 39: The words up to should start on a new linea line 39; "600 percent should read 6 .00

. percent,

d Column 7, line 7: "pf" should read of Column 8, line 30: A comma should be inserted between "percent" and "by".

a L .I

UNITED STATES PATENT OFFICE CERTIFICATE OF CGRRECTION Patent No. 3,929,495 Dated December 30, 1975 HEINZ BROEMER and NORBERT MEINERT It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below: O

r Page 2 of 2 '1 Column 8, line 34: "weightm" should read weight, Q

line 45: (B should read (B O line 62: "or" should read of Q Column 9, line 14: "B O should read (B 0 Column 10, line 16: A com should be inserted before up to Q Signed and Scaled this thirteenth Day of April1976 [SEAL] AIICSI.

RUTH C. MASON C. MARSHALL DANN Arresting Officer (ummissiuner uj'lareizts and Trademarks 

1. AN OPTICAL BORATE GLASS OF HIGH CHEMICAL RESISTANCE, WHICH NEGATIVE ANOMALOUS PARTIAL DISPERSION AND REFRACTIVE INDICES NE BETWEEN 1.65 AND 1.79 AND ABBE NUMBERS VE BETWEEN 40 AND 30, SAID GLASS CONSISTING OF BETWEEN 26 AND 39 PERCENT, BY WEIGHT, OF BORON TRIOXIDE (B2O3); BETWEEN 32 AND 57 PERCENT, BY WEIGHT, OF LEAD OXIDE (PBO); BETWEEN 5 AND 19 PERCENT, BY WEIGHT, OF ALUMINUM OXIDE (AL2O3); UP TO 3.0 PERCENT, BY WEIGHT, OF AT LEAST ONE OF THE OXIDES THE ALKALI METALS LITHIUM (LI), SODIUM (NA), AND POTASSIUM (K), BUT WHEN PERCENT, NOT LESS THAN 2.0 PERCENT, BY WEIGHT, OF SAID OOXIDES; UP TO 8.0 PERCENT, BY WEIGHT, OF ZINC OXIDE (ZNO), BUT, WHEN PERSENT, NOT LESS THSAN 0.8 PERCENT, BY WEIGHT, THEREOF, UP TO 600 PERCENT; BY WEIGHT, OF ZIRCONIUM DIOXIDE (ZRO2), BUT, WHEN PERSENT, NOT LESS THAN 2.0 PERCENT, BY WEIGHT, THEREOF; UP TO 15.0 PERCENT, BY WEIGHT, OF TANTALUM PENTOXIDE (TA2O5), BUT, WHEN PRESENT, NOT LESS THAN 2.0 PERCENT, BY WEIGHT, THEREOF; AND UP TO 16.0 PERCENT, BY WEIGHT, OF A OXIDE SELECTED FROM THE GROUP CONSISING OF ANTIMONY TRIOXIDE (SB2O3) AND BISMUTHUM TRIOXIDE (BI2O3), BUT WHEN PRESENT, NOT LESS THAN 8.0 PERCENT, BY WEIGHT, THEREOF.
 2. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3) and between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K).
 3. The glass of claim 1, consisting of betweeen 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3) and between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO).
 4. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), and between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO).
 5. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, pf lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3) and between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO2).
 6. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), and between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO2).
 7. The glasS of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO), and between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO2).
 8. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO), and between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO2).
 9. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), and between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta2O5).
 10. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3 ), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), and between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta2O5).
 11. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO), and between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta2O5).
 12. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO), and between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta2O5).
 13. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO2), and between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta2O5).
 14. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, Of aluminum oxide (Al2O3), between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO2) and between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta2O5).
 15. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO), between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO2), and between 2.0 and 15.0 percent by weight, of tantalum pentoxide (Ta2O5).
 16. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weightm of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO), between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO2), and between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta2O5).
 17. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2)3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), and between 8.0 and 16.0 percent, by weight, of at least one oxide selected from the group consisting of antimony trioxide (Sb2O3) and bismuthum trioxide (Bi2O3).
 18. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), betweeen 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO2), and between 8.0 and 16.0 percent, by weight, of at least one oxide selected from the group consisting of antimony trioxide (Sb2O3) and bismuthum trioxide (Bi2O3).
 19. The glass of claim 1, consisting of between 26 and 39 percent, by weight, or boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 2.0 and 15.0 percent, by weight, of tantalum pentoxide Ta2O5), and between 8.0 and 16.0 percent, by weight, of at least one oxide selected from the group consisting of antimony trioxide (Sb2O3) and bismuthum trioxide (Bi2O3).
 20. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO2), between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta2O5), and between 8.0 and 16.0 percent, By weight, of at least one oxide selected from the group consisting of antimony trioxide (Sb2)3) and bismuthum trioxide (Bi2O3).
 21. The glass of claim 1, consisting of between 26 and 39 percent, by weight, of boron trioxide B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), between 5 and 19 percent, by weight, of aluminum oxide (Al2O3), between 0.2 and 3.0 percent, by weight, of at least one of the oxides of the alkali metals selected from the group consisting of lithium (Li), sodium (Na), and potassium (K), between 0.8 and 8.0 percent, by weight, of zinc oxide (ZnO), between 2.0 and 6.0 percent, by weight, of zirconium dioxide (ZrO2), between 2.0 and 15.0 percent, by weight, of tantalum pentoxide (Ta2O5), and between 8.0 and 16.0 percent, by weight, of at least one oxide selected from the group consisting of antimony trioxide (Sb2O3) and bismuthum trioxide (Bi2O3).
 22. An optical borate glass of high chemical resistance of the following composition:
 23. In a process of manufacturing a glass of the composition of claim 1, the steps which consist essentially in a. melting a mixture of the oxides consisting of between 26 and 39 percent, by weight, of boron trioxide (B2O3), between 32 and 57 percent, by weight, of lead oxide (PbO), and between 5 and 19 percent, by weight, of aluminum oxide (Al2O3) up to 3.0 percent, by weight, of at least one of the oxides of the alkali metals lithium (Li), sodium (Na), and potassium (K), but, when present, not less than 2.0 percent, by weight, of said oxides; up to 8.0 percent, by weight, of zinc oxide (ZnO), but, when present, not less than 0.8 percent, by weight, thereof; up to 6.0 percent, by weight, of zirconium dioxide (ZrO2), but, when present, not less than 2.0 percent, by weight, thereof; up to 15.0 percent, by weight, of tantalum pentoxide (Ta2O5), but, when present, not less than 2.0 percent, by weight, thereof; and up to 16.0 percent, by weight, of an oxide selected from the group consisting of antimony trioxide (Sb2O3) and bismuthum trioxide (Bi2O3), but, when present, not less than 8.0 percent, by weight, thereof at a temperature between about 1300*C. and about 1500*C., b. homogenizing the molten mixture to produce a bubble-free melt, c. cooling said mixture to about 1120*C., and d. casting the melt into preheated molds. 